The technique of making a formed carbon structure by preforming a similarly shaped structure of a material which can be heated and decomposed into carbon is well known.
For instance, U.S. Pat. No. 3,264,073 to Schmitt teaches such a process as an intermediate step using phenolic microballoons manufactured, perhaps, according to the process disclosed in U.S. Pat. No. 2,976,574 to Keutgen et al. Other microballoons usable as a starting material are manufactured from pitch according to processes of a type recited in U.S. Pat. No. 3,786,134 to Amagi et al.
In order to decompose the formed degradable material into carbon and recover the carbon structure intact, the heating and cooling steps of the process are controlled as to temperature, temperature gradient and time in an inert atmospheric environment. Since the heating step raises the temperature well above the autoignition temperature in air for carbon, some known processes use a cooling step which is also carried out in an inert atmosphere, as taught for example in U.S. Pat. Nos. 3,121,050 to Ford, and 2,461,365 to Bennett et al.
The prior art suggests a number of pyrolytically degradable materials for use as initial preformed microballoons, for instance polymers of alkyd or phenol resins or polyurethanes as suggested in Chemical Abstracts, Vol. 73, 1970, page 36, abstract 110,604q, or starting with an aromatic pitch as suggested in U.S. Pat. No. 3,786,134 (supra).